The present invention relates generally to Integrated Gasification Combined Cycle (IGCC) power plants, and more specifically to methods and apparatus for using diluent nitrogen with dry syngas in IGCC plants.
In at least some known IGCC plants and in certain operating conditions, diluent is mixed with syngas to improve the mass flow through a combustor. Nitrogen process gas from an air separator is commonly used as diluent. When additional diluent is needed, the syngas is saturated with water vapor, which acts as an additional diluent. However, the addition of water vapor in the syngas may cause variations in the heating value of the syngas. Such variations can lead to variances in firing temperature, and/or may adversely affect the performance and/or efficiency of the combustor. Moreover, moisture in the syngas adversely lowers the combustor firing temperature and combustor efficiency. As such, the possible adverse affects of the addition of water vapor may outweigh any benefits.
Thus, methods and apparatus to supply diluent to the combustor are desirable to maintain a constant heating value of the syngas. Maintaining a constant heating facilitates the combustor maintaining a constant firing temperature such that the combustor's performance and efficiency is also maintained. In addition, methods and apparatus to supply diluent to the combustor so that dry syngas can be burned efficiently are desirable to raise the combustor firing temperature and further enhance the combustor's performance and efficiency. Also desirable are methods and apparatus to facilitate enhancing the use of waste process heat to increase the efficiency of IGCC plants.